Question

专家，

以下是我的代码，

问题描述：db.execSQL语句发生错误，表示null db object。

我试着检查出了什么问题，并且应用了2个toast，发现“test”没有显示，我理解这意味着checkSelfPermission判断为false，所以我已经获得了许可。但是如果我直接编写db = SQLiteDatabase.openOrCreateDatabase（），它将会出现“未知错误（代码14）：无法打开数据库”。

我真的不知道，请提前帮助，谢谢。

ActivityCompat.checkSelfPermission(this,
            Manifest.permission.WRITE_EXTERNAL_STORAGE)
            != PackageManager.PERMISSION_GRANTED

代码：

public class AbcActivity extends Activity {

SQLiteDatabase db;

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);

    switch (requestCode) {
        case 111222:
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
                db = SQLiteDatabase.openOrCreateDatabase(Global.dataFolder + File.separator + "xxxxx", null);
            else {
                System.exit(0);
            }
            break;
    }
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_param);

    if (ActivityCompat.checkSelfPermission(this,
            Manifest.permission.WRITE_EXTERNAL_STORAGE)
            != PackageManager.PERMISSION_GRANTED) {
        Toast.makeText(getApplicationContext(), "test", Toast.LENGTH_SHORT).show();

        if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.WRITE_EXTERNAL_STORAGE))
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                    111222);
        else
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                    111222);
    }
    Toast.makeText(getApplicationContext(), "test2", Toast.LENGTH_SHORT).show();

    //db = SQLiteDatabase.openOrCreateDatabase(Global.dataFolder + File.separator + "xxxxx", null);
    db.execSQL("create table if not exists " + "xxxxx" + "(" +
            //<editor-fold desc="columns">
            "DtdKink REAL," +
            "TttBin REAL" +
            //</editor-fold>
            ")");
}

}

Answer 1

我认为它与权限无关，您应该使用MariaDB [dev]> SELECT postcode, ( 3959 * acos( cos( radians( 53.1852582 ) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians(-3.0198408999999997) ) + sin( radians(53.1852582) ) * sin( radians( latitude ) ) ) ) AS distance -> FROM uk_postcodes -> ORDER BY distance ASC -> LIMIT 1; +----------+---------------------+ | postcode | distance | +----------+---------------------+ | CH5 3PF | 0.13510896180231324 | +----------+---------------------+ 1 row in set (3.10 sec)类来使用SQLite。

示例：

SQLiteOpenHelper

来自：

的信息

https://developer.android.com/training/basics/data-storage/databases.html

编辑：

在API 23中，当您尝试在外部存储中创建文件夹时，openOrCreateDatabase（）不会创建该文件夹，请在调用此方法之前尝试执行该文件夹

检查此解决方案：

public class FeedReaderDbHelper extends SQLiteOpenHelper {
    // If you change the database schema, you must increment the database version.
    public static final int DATABASE_VERSION = 1;
    public static final String DATABASE_NAME = "FeedReader.db";

    public FeedReaderDbHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_ENTRIES);
    }
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // This database is only a cache for online data, so its upgrade policy is
        // to simply to discard the data and start over
        db.execSQL(SQL_DELETE_ENTRIES);
        onCreate(db);
    }
    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        onUpgrade(db, oldVersion, newVersion);
    }
}

如何为Android API 23授予运行时权限？

1 个答案: